It is possible to save the unviewed images.
The newest version of the SnapChat-App encrypt the images.
But you can easily decrypt them.
The App use an AES 128bit encryption algorithm with a 16 char long key.

We've had a few cases in recently with snapchat. I found a ruby script that would decrypt the encrypted images and movies and then just edited it a bit to parse through a folder to decrypt and rename the files for viewing. The script is as follows:-